The field of the disclosure relates generally to direct current (DC) transmission systems and, more particularly, to medium voltage DC (MVDC) and high voltage DC (HVDC) converter systems and methods of operation thereof.
At least some of known electric power transmission and distribution facilities are physically positioned in a remote geographical region or in an area where physical access is difficult. One example includes electric power transmission and distribution facilities geographically located in rugged and/or remote terrain, for example, mountainous hillsides, extended distances from electric power grids, and submerged, e.g., off-shore oil and gas exploration and recovery installations. Many of these known electric power transmission and distribution facilities include a separated power conversion assembly, or system, electrically coupled to an alternating current (AC) power source. Such known separated power conversion assemblies include a rectifier portion that converts the AC generated by the power generation facilities to direct current (DC) and an inverter portion that converts the DC to AC of a predetermined frequency and voltage amplitude. The rectifier portion of the separated power conversion assembly is positioned in close vicinity of the associated AC power source and the inverter portion of the separated full power conversion assembly is positioned in close vicinity of the powered loads. Such rectifier and inverter portions are typically electrically coupled via a MVDC or a HVDC link, e.g., a MVDC electric power distribution system or a HVDC electric power transmission system.
Since many of the known separated power conversion assemblies are remotely positioned, they are protected against accelerated reductions in service life due to short circuits, on the AC side and the DC link side through a variety of means. One method includes opening associated circuit breakers to isolate the affected power conversion assembly, thereby interrupting the current flow with the effect of de-energizing all downstream loads for an indeterminate period of time. Also, at least some of the known power conversion assemblies include oversized, more robust, and more costly components than would otherwise be necessary for easily accessible and redundant devices. Further, at least some of the known power conversion assemblies attempt to limit the current flow through the converter components by devices positioned in series with the principle current path using one of inductive devices, AC breakers, DC breakers, and reverting the polarity of the full bridge cells resident in the power converters.